If you follow the current timeline, it should go-
Hurt->Eccleston->Tennant->Tennant->Smith->Capaldi->Whitaker->Tennant->Tennant/Gatwa
Hurt was the real 9th doctor, but we call Eccleston the 9th doctor. And (if I get this all right) Tennant regenerated as himself twice, so he should be the 11th, 12th, 15th and Doctor 16 and a half. But people call him the 10th doctor. And Jodie Whitaker should have been the 14th Doctor, but people call her the 13th Doctor. And then Tennant came back and then there was the bigeneration of him and Gatwa.
And just to add to it all, there’s also a female clone of Tennant out there somewhere.
Is anyone else as confused as I am?
EDIT: Oh god, I just realized it gets even more confusing because now there’s all the Doctors before Hartnell.
You seem insistent on overcomplicating things that have explanation easily at hand. Hurt isn’t counted because the character relinquished the title for the period of time that he existed. Tennant is only 10th and 14th. The metacrisis Doctor was not the Doctor, they weren’t even Timelord. And Gatwa isn’t “sharing” the current generation. The bi-generation is best explained as time loop - 14 will continue to live and emotionally heal, and at some point will regenerate into 15, who pops up where they’re introduced in the show (ie “doing rehab out of order”). And to your last point, Jo Martin’s Doctor pre-dates the current cycle, which is pretty plainly established by Chibnall themselves, so I’m pretty sure they understand it.
To keep it even more simple, just believe the show runners when they say which iteration is which instead of deciding they’re wrong about the show they are making for reasons that have already been explained.